Laser beam machining method with interrupt and restart functions

ABSTRACT

A method for irradiating a workpiece making a relative move in accordance with a work program with a laser beam for cutting the workpiece includes steps of interrupting the cutting being executed and then restarting the cutting. As the cutting is restarted, machining of the workpiece is performed under specified conditions for a predetermined distance and a predetermined time to provide sufficient machining of the workpiece.

This is a divisional of application Ser. No. 08/589,877 filed Jan. 23,1996 now U.S. Pat. No. 5,847,359.

BACKGROUND OF THE INVENTION

This invention relates to a laser beam machining system using a laserbeam for cutting a workpiece and more particularly to an improvement inwork failure at the work restart time after the work is interrupted.

FIG. 18 shows the configuration of a laser beam machine system. In acontroller 1, a CPU (central processing unit) 2 reads a work programstored in a RAM 4 (random access memory) based on a control programstored in a ROM 3 (read-only memory) and controls the entire laser beammachining system. The RAM 4 stores work condition data, etc. in additionto the work programs. An I/O unit 5 converts a control signal outputfrom the CPU 2 and sends the resultant control signal to a laseroscillator 6, which then performs emission, stopping, output change,etc., of a laser beam 7 in response to the received control signal. Thelaser beam 7 is sent via a mirror 8 to a laser beam machine 9.

The laser beam machine 9 is provided with a table to which a workpiece10 is fixed and a work head 12 for irradiating the workpiece 10 with alaser beam. The laser beam 7 introduced into the work head 12 isgathered by a light gatherer disposed in the work head and is applied tothe workpiece 10 through a nozzle 12a. At the same time, a work gas (notshown) is also sprayed to the workpiece through the nozzle. The laserbeam machine 9 is provided with servo motors 13 and 14 for performingmove control of the table 11 in two directions of X and Y axes. Theservo motors 13 and 14 are connected to servo amplifiers 15 and 16respectively in the controller 1 and are subjected to rotation controlthrough the amplifiers in response to a control signal issued from theCPU 2. A move system in the Z axis direction for controlling the focusposition of the laser beam applied to the workpiece 10 also exists, buthere is omitted. Commands are given to the laser beam machining systemand parameters are set for the system through a CRT/MDI unit 17.

FIG. 19 is a functional block diagram of the conventional laser beammachining system. The functions and configuration of the blocks will bediscussed with reference to FIG. 19. In the controller 1, a programanalysis section 18 analyzes the instruction contents of a work programand issues a command to a move command section 19 or a work conditioncommand section 20. When receiving a work condition command from theprogram analysis section 18, the work condition command section 20 callswork condition data responsive to the command from a work conditionregistration section 21 and sets work conditions. If work conditionvalues are specified directly in the program, the values are handledlike the work condition data and the work conditions are set. The workcondition data is data of piercing conditions, cutting conditions, etc.,set in response to workpiece material and its plate thickness, such aslaser output, duty, frequency, piercing time, etc., set as laseroscillator work conditions and speed set as a move condition of thelaser beam machine for making a relative move of a workpiece withrespect to a laser beam. If a move command is received from the programanalysis section 18, the move command section 19 generates a traveldistance from the work programmed path and setup work condition speed.An interrupt/restart determinating section 22 determines emergency stopto be caused by alarm occurrence, factitious temporary stop to bespecified by a feed hold command, work restart to be specified by a workrestart command such as the subsequent cycle start command, etc., andbased on the determination, sends a stop/restart determination signal tothe move command section 19 and the work condition command section 20.When receiving the stop/restart determination signal, the move commandsection 19 and the work condition command section 20 generate a movecommand and a work condition command and output them to the laseroscillator 6 and the laser beam machine 9.

FIG. 20A shows a work program example for the laser beam machiningsystem and FIG. 20B shows a work process flow corresponding to the workprogram. The work operation will be discussed with reference to FIG. 20.

The program analysis section 18 analyzes the command on work programline N01 (piercing condition selection command) and outputs the piercingcondition selection command. When receiving the piercing conditionselection command, the work condition command section 20 calls piercingcondition data stored in the work condition registration section 21 andsets piercing conditions at step S100 (the piercing is to make a hole atthe work start time and the piercing condition data is laser output,duty, frequency, piercing time, etc.,). Likewise, the program analysissection 18 analyzes the command on work program line N02 (piercingexecution command) and outputs the piercing execution command. Inputtingthe piercing execution command, the work condition command section 20outputs a laser beam irradiation signal to the laser oscillator andwaits for the piercing time set in the piercing conditions at step S101.Meanwhile, a through hole is made (completion of the piercing).Likewise, the program analysis section 18 analyzes the command on workprogram line N03 (cutting condition selection command) and outputs thecutting condition selection command. Inputting the cutting conditionselection command, the work condition command section 20 calls cuttingcondition data and sets cutting conditions at step S102. Likewise, theprogram analysis section 18 analyzes the commands on work program linesN04 to N98 (move commands for moving the table in response to the cutshape) and outputs the move commands. Inputting the move commands, themove command section 18 drives the servo motors for moving the table atthe speed set in the cutting conditions at step S103. As a result, theworkpiece is cut to a desired shape. Subsequently, the program analysissection 18 analyzes the command on work program line N99 (cutting endcommand) and outputs the cutting end command. Inputting the cutting endcommand, the work condition command section 20 turns off the laser beamand work gas at step S104. Working of one workpiece is now complete.

If a temporary stop command is given due to alarm occurrence or by afeed hold command during the cutting following the program path (stepS103), the interrupt/restart determinating section receives thetemporary stop signal and outputs a work interrupt determination signal.When receiving the work interrupt determination signal, the move commandsection outputs a stop command for stopping the table move and the workcondition command section outputs a stop command for stoppingirradiation with the laser beam, spraying of the work gas, etc. Uponreception of the stop commands, the laser beam machining is stopped.Then, if a work continuation command is given by a cycle start command,the laser beam machining is restarted.

FIG. 21 shows a process flow at the work restart time. The operation atthe restart time will be discussed with reference to FIG. 21. When awork restart command is given, the interrupt/restart determinatingsection receives the work restart command, determines work restart, andoutputs a work start determination signal. Inputting the work startdetermination signal, the work condition command section restores thestate required for the work gas spraying, laser beam irradiation, etc.,to the state before the temporary stop (containing the work conditions)at step S105. Next, the move command section outputs a restart movecommand at step S106 and the cutting is restarted.

FIG. 22 is an illustration showing how laser cutting is performed. Whencutting of the workpiece 10 by the laser beam 7 proceeds, a bottom face10b of the workpiece 10 lags in the cutting progress behind a top face10a (m shown in FIGS. 22 and 23). The thicker the workpiece and thefaster the work speed, the more remarkable the tendency (as shown inFIG. 23). Therefore, if a temporary stop command is given during thecutting and the working is stopped, the top face of the workpiece iscut, but uncut portion m remains in the bottom face at the stopposition. After this, if a work restart command is given in the stateand the cutting is started in the same cutting conditions as before thestop, a flow of molten metal at the start time worsens because of theuncut portion m in the cutting restart part; work failure easily occurs.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a laser beammachining system which can select optimum work conditions at a restartpoint and restart cutting when restarting cutting after temporary stopof cutting containing emergency stop. For reference, FIG. 23 is anillustration as to how the lag amount indicated by distance m in FIG. 22varies depending on the plate thickness and cutting speed with two platethicknesses of soft steel material (hatched portions denote variations).

To this end, according to the invention, there is provided a laser beammachining system comprising a controller, a laser oscillator forgenerating and outputting a laser beam upon reception of a work commandfor laser oscillation from the controller, and a laser beam machine forreceiving the laser beam, gathering it, and irradiating a workpiece withthe gathered laser beam and upon reception of a work command for a workpath move from the controller, the laser beam machine for making arelative move of the workpiece with respect to a work head, thecontroller comprising a program analysis section for analyzing a workprogram in accordance with a control program procedure and generatingand outputting work program commands, a work condition registrationsection for storing work condition data of piercing, cutting, restartwork, etc., and selectively outputting the work condition data inresponse to a request, a work command section, upon reception of thework program command, for calling the corresponding work condition datafrom the work condition registration section and generating andoutputting the work command for laser oscillation and the work commandfor a work path move, and a restart command section, when outputting arestart command to the work command section and generating a restartwork command upon reception of a restart signal for releasing a stopstate, for calling work condition data for restart work from the workcondition registration section in conjunction with the work commandsection, using the work condition data to correct a work command basedon a work program command after the stop, and causing the work commandsection to output the corrected work command.

The restart command section in the laser beam machining system comprisesa restart command section for determining a work restart signal,generating a restart command, outputting it to the work command sectionfor calling the work condition data for restart work from the workcondition registration section, using the work condition data to correcta work command based on a work program command after the stop, andoutputting the corrected work command as a restart work command, a movedistance calculation section, upon reception of the restart command andthe restart work command, for adding up work path move distances andoutputting the result value, a distance setting section for outputtingdistance L1 for restart work preset therein in response to a request,and a move distance comparison section, upon reception of the resultvalue, for calling the distance L1 and comparing it with the resultvalue and if they match, the move distance comparison section foroutputting a restart work distance match signal to the work commandsection for causing the work command section to terminate generation ofthe restart work command and return to motion in accordance with thework program commands.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed and restart the cutting at theinterrupt position, the method comprising the steps of:

after the restart, working on a move path specified in the work programat a predetermined distance L1 under restart work conditions, andchanging the restart work conditions to original work conditions forcontinuing the cutting.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed and restart the cutting at theinterrupt position, the method comprising the steps of:

after the restart, working on a moving path specified in the workprogram at a predetermined distance L1 under restart work conditions,after working at the predetermined distance L1, returning the workposition to the work restart position, and changing the restart workconditions to original work conditions for continuing the cutting.

According to the invention, there is provided a laser beam machiningsystem comprising a controller, a laser oscillator for generating andoutputting a laser beam upon reception of a work command for laseroscillation from the controller, and a laser beam machine for receivingthe laser beam, gathering it, and irradiating a workpiece with thegathered laser beam and upon reception of a work command for a work pathmove from the controller, the laser beam machine for making a relativemove of the workpiece with respect to a work head, the controllercomprising:

a program analysis section for analyzing a work program in accordancewith a control program procedure and generating and outputting workprogram commands;

a work condition registration section for storing work condition data ofpiercing, cutting, restart work, etc., and selectively outputting thework condition data in response to a request;

a work command section, upon reception of the work program command, forcalling the corresponding work condition data from the work conditionregistration section and generating and outputting work commands foroperating the laser oscillator and the laser beam machine;

a restart command section, when outputting a restart command to the workcommand section and generating a restart work command upon reception ofa restart signal for releasing a stop state, for calling work conditiondata for restart work from the work condition registration section inconjunction with the work command section, using the work condition datato correct a work command based on a work program command after thestop, and causing the work command section to output the correctedrestart work command; and

a cooling command section for stopping a work command based on the workprogram for a predetermined time in conjunction with the work commandsection after the restart work command.

The cooling command section in the laser beam machining system comprisesa timer for starting counting up the elapsed time since output of therestart work command and outputting the count time, a time settingsection in which time T1 is previously stored, and a stop timecomparison section, upon reception of the count time output from thetimer, for comparing the time with the time T1 called from the timesetting section and if they match, the stop time comparison section foroutputting a match signal to the work command section for returning tomotion following work program commands after the restart work command.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed and restart the cutting at theinterrupt position, the method comprising the steps of:

after the restart, working on a moving path specified in the workprogram at a predetermined distance L1 under restart work conditions,after working at the predetermined distance L1, returning the workposition to the work restart position, continuing to irradiate thereturn position with a laser beam for a predetermined time, and changingthe restart work conditions to original work conditions for continuingthe cutting.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed and restart the cutting at theinterrupt position, the method comprising the steps of:

after the restart, working under restart work conditions without a movefor a predetermined time, and changing the restart work conditions tooriginal work conditions for continuing the cutting.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed, the method comprising the step of,at the interrupt time, continuing to irradiate the position with a laserbeam for a predetermined time under interrupt work conditions and theninterrupting the work.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, tointerrupt the cutting being executed and restart the cutting at theinterrupt position, the method comprising the steps of:

cutting the workpiece while making a backward move of a moving pathbefore the interrupt specified in the work program by a predetermineddistance under backward move work conditions, and continuing cutting theworkpiece again in an original cutting direction under original workconditions.

According to the invention, there is provided a laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, themethod comprising the step of:

when a work condition is changed from a low-output laser beam to ahigh-output laser beam, stopping a work path move for a predeterminedtime and then irradiating the workpiece with the high-output laser beam.

In the laser beam machining system (aspect 1), when outputting a restartcommand to the work command section and generating a restart workcommand upon reception of a restart signal after a stop command, therestart command section calls work condition data for restart work fromthe work condition registration section in conjunction with the workcommand section, uses the work condition data to correct a work commandbased on a work program command after the stop, and causes the workcommand section to output the corrected work command.

The restart command section in the laser beam machining system (aspect2) determines a work restart signal, outputs a restart command to thework command section, and causes the work condition registration sectionto output a restart work command, the move distance calculation sectionadds up move command distances from the restart work command and outputsthe result value, and the move distance comparison section compares theresult value with a predetermined distance L1 and if they match, outputsa restart work distance match signal to the work command section forcausing the work command section to terminate generation of the restartwork command and return to motion in accordance with the work programcommands.

The laser beam machining method for irradiating a workpiece making arelative move in accordance with a work program with a laser beam forcutting the workpiece (aspect 3), to interrupt the cutting beingexecuted and restart the cutting at the interrupt position, comprisingthe steps of:

after the restart, working on a moving path specified in the workprogram at a predetermined distance L1 under restart work conditions,and changing the restart work conditions to original work conditions forcontinuing the cutting.

The laser beam machining method (aspect 4) comprises the first step ofworking at a predetermined distance L1 under restart work conditionsafter the restart and the second step of returning the work position tothe work restart position.

When outputting a restart command to the work command section andgenerating a restart work command upon reception of a restart signal,the restart command section in the laser beam machining system (aspect5) uses work condition data for restart work to correct a work commandbased on a work program command after the stop in conjunction with thework command section and causes the work command section to output thecorrected work command, and the cooling command section stops a workcommand based on the work program for a predetermined time inconjunction with the work command section after the restart workcommand.

The cooling command section in the laser beam machining system (aspect6) uses the timer to count up the elapsed time since output of therestart work command and output the count time, and the stop timecomparison section compares the count time with the time T1 called fromthe time setting section and if they match, outputs a match signal tothe work command section for returning to motion following work programcommands after the restart work command.

The laser beam machining method (aspect 7) comprises the first step ofcutting the moving path specified in the work program at a predetermineddistance under restart work conditions, the second step of returning thework position to the work restart position, and the third step ofstabilizing laser beam output for cutting.

The laser beam machining method (aspect 8) comprises the first step ofirradiating the workpiece with a laser beam under restart workconditions without a move for a predetermined time to remove the bottomface work lag.

The laser beam machining method (aspect 9) comprises the step ofirradiating the position at the interrupt time with a laser beam for apredetermined time under interrupt work conditions to remove the bottomface work lag and then interrupting the work.

The laser beam machining method (aspect 10) comprises the first step ofcutting the workpiece while making a backward move of a moving pathbefore the interrupt by a predetermined distance under backward movework conditions, and the second step of continuing cutting the workpieceagain in an original cutting direction under original work conditions tomake the cut work surface continuous.

The laser beam machining method (aspect 11) comprises the step of, whena work condition is changed from a low-output laser beam to ahigh-output laser beam, stopping a work path move for a predeterminedtime and then irradiating the workpiece with the high-output laser beamto stabilize the laser beam output.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a functional block diagram of a first embodiment of theinvention;

FIG. 2 is a work process flowchart according to the first embodiment ofthe invention;

FIG. 3 is a drawing showing how to work on a workpiece according to thefirst embodiment of the invention;

FIG. 4 is a work process flowchart according to a second embodiment ofthe invention;

FIG. 5 is a drawing showing how to work on a workpiece according to thesecond embodiment of the invention;

FIG. 6 is a functional block diagram of a third embodiment of theinvention;

FIG. 7 is a work process flowchart according to the third embodiment ofthe invention;

FIG. 8 is a drawing showing how to work on a workpiece according to thethird embodiment of the invention;

FIG. 9 is a work process flowchart according to a fourth embodiment ofthe invention;

FIG. 10 is a drawing showing how to work on a workpiece according to thefourth embodiment of the invention;

FIG. 11 is a work process flowchart according to a fifth embodiment ofthe invention;

FIG. 12 is a drawing showing how to work on a workpiece according to thefifth embodiment of the invention;

FIG. 13 is a work process flowchart according to a sixth embodiment ofthe invention;

FIG. 14 is a drawing showing how to work on a workpiece according to thesixth embodiment of the invention;

FIG. 15 is a work process flowchart according to a seventh embodiment ofthe invention;

FIG. 16 is a drawing showing how to work on a workpiece according to theseventh embodiment of the invention;

FIG. 17 is a registered work condition data example showing an eighthembodiment of the invention;

FIG. 18 is a block diagram of a laser beam machining system;

FIG. 19 is a functional block diagram of the conventional laser beammachining system;

FIG. 20A is a work program example for the laser beam machining systemand FIG. 20B is a process flow chart corresponding thereto;

FIG. 21 is a conventional process flowchart at the work restart time;

FIG. 22 is an illustration showing how laser beam machining isperformed; and

FIG. 23 is a graph showing lag amount change of a front face dependingon the plate thickness and cutting speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, there are shown preferredembodiments of the invention.

(Embodiment 1)

FIG. 1 is a functional block diagram of a laser beam machining systemaccording to a first embodiment of the invention. The configuration ofthe embodiment will be discussed with reference to FIGS. 1 and 18.

The laser beam machining system consists of a controller 1, a laseroscillator 6, and a laser beam machine 9. The laser oscillator 6 and thelaser beam machine 9 operate based on commands of the controller 1 andfeed back their operation state to the controller 1.

The controller 1 consists of a work command section 100 comprising aprogram analysis section 18, a work condition registration section 21, amove command section 19, and a work condition command section 20 and arestart command section 200 comprising an interrupt/restartdetermination section 22, a move distance calculation section 23, a movedistance comparison section 24, and a distance setting section 25.

The program analysis section 18, which is made up of a CPU 2, a ROM 3for storing a control program, a RAM 4 for storing work programs, etc.,analyzes the contents of a work program according to the control programprocedure and outputs the analysis results as work program commandsincluding moving path commands, work condition commands, etc.

The work command section 100 comprising the move command section 19 andthe work condition command section 20 is made up of the CPU 2, an I/Ounit 5, servo amplifiers 15 and 16, etc. Upon reception of a workprogram command, such as a moving path command or a work conditioncommand, output by the program analysis section 18, the work commandsection 100 calls the work condition data corresponding to the commandfrom the work condition registration section 21. The work conditioncommand section 20 generates and outputs work commands (laseroscillation commands) containing laser output, duty, frequency, etc.,for operating the laser oscillator 6. The move command section 19generates and outputs work commands (laser beam machining commands)containing the amount, speed, etc., for operating servo motors 13 and 14of the laser beam machine 9.

If work condition values are specified directly in a work program, theyare handled as work condition data.

Until completion of restart working after reception of a restart commandsignal (described below) output from the restart command section 200,the work command section 100 in conjunction with the restart commandsection 200 generates and outputs work commands including a laseroscillation command, laser beam machining command, etc., for restartworking, as discussed below in detail.

The work condition registration section 21 consists of components suchas the RAM 4 for storing work condition data and a CRT/MDI unit 17 whichserves as an input section and a display section of conditions such aswork condition data, and selectively outputs work condition data basedon a request made by the work command section 100. The work conditiondata includes first to third condition groups, etc., shown in FIG. 17;optimum data is input depending on the material and plate thickness of aworkpiece 10.

The restart command section 200 comprising the interrupt/restartdetermination section 22, the move distance calculation section 23, themove distance comparison section 24, and the distance setting section 25is made up of the CPU 2, the ROM 3, the RAM 4, etc. Theinterrupt/restart determination section 22 determines temporary stop tobe caused by alarm occurrence or specified by a feed hold command andwork restart to be specified by the subsequent cycle start command, andsends the determination to the work command section 100 (the movecommand section 19 and the work condition command section 20) and themove distance calculation section 23. The move distance calculationsection 23 calculates the move distance in a work command (move command)after the interrupt/restart determination section 22 determines workrestart. The move distance comparison section 24 compares the movedistance calculated by the move distance calculation section 23 withdistance L1 preset in the distance setting section 25 for determiningwhether or not the move made after the work restart has proceeded apredetermined distance. If they match, the move distance comparisonsection 24 sends a match signal to the work command section 100 (themove command section 19 and the work condition command section 20). Thework command section 10 generates a move command and a work conditioncommand not contained in the original work program in response to theinformation provided by the interrupt/restart determination section 22and the move distance comparison section 24.

FIG. 2 is a process flowchart at the work restart time showing theembodiment of the invention. The operation will be discussed withreference to the figure. If a work restart command is given aftertemporary stop of work, the work command section 100 (work conditioncommand section 20) calls and sets work condition data for work restartat step S200 in response to work restart information provided by theinterrupt/restart determination section 22. For the work restartconditions, low-speed, low-output, low-frequency pulse dedicatedconditions for enabling cutting even if a cut lag part in the bottomface of the workpiece exists are registered in the work conditionregistration section 21 (RAM 4) as the work condition data. Cutconditions at the work stop time are saved before change to theconditions applied at the work restart time is made. Next, the workcondition command section 20 restores the functions required for worksuch as work gas spraying and laser beam irradiation to the state beforethe temporary stop at step S201. The sprayed work gas pressure andapplied laser beam output at the time become the condition values setfor the work restart. The move command of the work command section 100(move command section 19) causes a move to be restarted and made by thepredetermined distance L1 at step S202. This means that the workpiece iscut by the distance L1 under the work restart conditions. While theworkpiece is cut under the low-speed work restart conditions, the bottomface cut lag behind the top face of the workpiece lessens. The distanceL1 set in the distance setting section 25 is a cut distance required bythe time the lag sufficiently lessens. Inputting the information"distance L1 move after work restart" from the move distance comparisonsection 24, the work command section 100 (work condition command section20) sets the stored original cutting conditions at step S203. Then, thework command section 100 (move command section 19) outputs a workcommand for continuing the interrupted cutting under the originalcutting conditions at step S204.

FIG. 3 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) cut the workpiece 10 following the program path by distance L1 underwork restart conditions; and

(3) cut the workpiece 10 under the original work conditions.

Thus, according to the embodiment, after a work interrupt command isreceived during working in accordance with the work program, to restartthe interrupted work, work conditions appropriate for restart work areautomatically generated and the work is restarted by the distance L1under the generated conditions rather than restarting under the workconditions applied at the work interrupt time specified in the workprogram. Therefore, after the bottom face cut lag behind the top face ofthe workpiece is lessened, cutting can be continued; work failure at therestart work time can be prevented.

(Embodiment 2)

FIG. 4 is a process flowchart at the work restart time showing a secondembodiment of the invention. In the first embodiment, after the bottomface cut lag behind the top face of the workpiece is lessened, cuttingcan be continued; if the plate thickness increases, the bottom face cutlag does not entirely disappear even under the low-speed work restartconditions. Particularly, if the work speed of the cut condition isfast, it is necessary to smooth a flow of molten metal in the cutstarting portion. The second embodiment of the invention is suitable forsuch a purpose. The operation will be discussed.

Steps S106 and S200 to S203 in FIG. 4 are the same as those in FIGS. 21and 2. Inputting the information "distance L1 move after work restart"from a move distance comparison section, a work condition commandsection temporarily stops irradiation with a laser beam at step S205. Todo this, a laser beam irradiation stop signal may be output to a laseroscillator or an output command is set to 0. A move command sectionmoves a table for returning the work position to the work stop positionat step S206. Next, the work condition command section sets the storedoriginal cut conditions at step S203 and irradiation with a laser beamis restarted at step S207. After this, the move command section restartsa move at step S106. The already cut L1 portion is passed through andcutting is continued.

FIG. 5 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) cut the workpiece 10 following the program path by distance L1 underwork restart conditions;

(3) stop irradiation with a laser beam and return to position A; and

(4) irradiate the workpiece 10 with a laser beam for cutting theworkpiece 10 under the original work conditions.

According to the embodiment, work conditions appropriate for restartwork are automatically generated and the work is restarted by thedistance L1 under the generated conditions and then the work position isreturned to the interrupt position for restarting the cutting under theoriginal work conditions. Therefore, after the bottom face cut lagbehind the top face of the workpiece is lessened, cutting can becontinued; work failure at the restart work time can be prevented. Inaddition, the cut starting portion becomes a work finish face asprovided as if the cutting were continued nonstop.

(Embodiment 3)

FIG. 6 is a functional block diagram of a laser beam machining systemaccording to a third embodiment of the invention. A flow of molten metalis smoothed as if work continued nonstop according to the secondembodiment. However, if heat of the workpiece much accumulates at thework stop time, there is the possibility of work failure. The thirdembodiment is provided for taking countermeasures against it.

Blocks 18 to 25 in FIG. 6 are the same as those in FIG. 1 and will notbe discussed again. A cooling command section 201 receives commandinformation indicating work completion at distance L1 in restart workfrom a work command section 100 (work condition command section 20) andmeasures the time with a timer 26 in response to the command. A timecomparison section 27 compares the measured time with time T1 preset ina time setting section 28 and if they match, sends a cooling end commandto the work command section 100 (move command section 19 and workcondition command section 20). Upon reception of the command, the workcommand section 100 restarts cutting under the cut condition applied atthe interrupt time.

FIG. 7 is a process flowchart of the embodiment of the invention. StepsS200 to S207 and S106 in FIG. 7 are the same as those in FIG. 4. Thelaser beam irradiation stop time is measured with the timer 26 and atstep S208, the workpiece is cooled until a lapse of the time T1 set bythe time setting section. To do this, a cooling material spray dedicatedto cooling may be attached or simply spraying a work gas has the effectof cooling because irradiation with a laser beam stops. Cooling at stepS208 may be executed before a return to the restart position at stepS206 if laser beam irradiation stops.

FIG. 8 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) cut the workpiece 10 following the program path by distance L1 underwork restart conditions;

(3) stop irradiation with a laser beam and return to position A;

(4) cool the workpiece 10 as long as time T1; and

(5) irradiate the workpiece 10 with a laser beam for cutting theworkpiece 10 under the original work conditions.

According to the embodiment provided by adding the cooling commandsection 201 to the first or second embodiment, the cooling period of thetime T1 is provided after execution of restart work at distance L1 atthe restart work time. Therefore, the embodiment has the effect ofpreventing overheating from causing work failure in addition to theeffects of the first and second embodiments.

(Embodiment 4)

FIG. 9 is a process flowchart of a fourth embodiment of the invention.The embodiment is provided for an alternative method for uncut portiontreatment in the bottom face of a workpiece at the work stop position.The operation will be discussed. Steps S200 to S203 and S106 in FIG. 9are the same as those in FIG. 4 except for restart work conditionsselected at step S200. The restart work conditions selected at step S200in FIG. 9 are set for irradiating the workpiece with a laser beam at theposition to remove an uncut portion. For example, piercing conditionsare applied. The laser beam irradiation time is measured with a timer 26and moving stops at the position as long as predetermined time T2 withthe workpiece irradiated with a laser beam, etc., under the conditionsat step S209. Meanwhile, removing the uncut portion is completed. Then,the original cut conditions are selected at step S203 and the cutting isrestarted at step S106. If condition change in the first to thirdembodiments is also used in the cut starting portions at steps S203 andS106, furthermore the effect of preventing work failure is produced.

FIG. 10 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) irradiate the workpiece 10 with a laser beam at the position as longas the time T2 under the work restart conditions; and

(3) cut the workpiece 10 under the original work conditions.

According to the embodiment, the remaining portion in the bottom face ofthe workpiece at the cutting interrupt time is treated at the workrestart time under appropriate piercing conditions before the work isexecuted. Therefore, work failure at the work restart time can beprevented and if the embodiment is combined with the first to thirdembodiments, work failure is furthermore reduced.

(Embodiment 5)

FIG. 11 is a process flowchart at the work stop time in a fifthembodiment of the invention. In the embodiment, when a work stop commandis received, an uncut portion in the bottom face of a workpiece isremoved before the work is stopped. When a work stop command is given, amove command section stops the move at step S210 in response to workinterrupt information from an interrupt/restart determination section.When the move stops, a work condition command section calls and setswork conditions applied at the work stop time at step S211. The workconditions applied at the work stop time are set for removing a cut lagportion in the bottom face of a workpiece made at the move stop time;for example, piercing conditions are applied. Cut conditions at the workstop time are saved before change to the conditions applied at the workstop time is made. The time after changing to the conditions applied atthe work stop time is measured with a timer 26 and a wait is made forpredetermined time T3 at step S212. Meanwhile, the uncut portion isremoved. Next, the work condition command section stops irradiating witha laser beam, spraying a work gas, etc., at step S213. Then, the storedoriginal cut conditions are set at step S203, whereby when the work isrestarted, the uncut portion in the bottom face of the workpiece hasbeen removed, so that work failure can be prevented. However, when it isnecessary to immediately stop laser beam irradiation to stop the workdue to an alarm, etc., a wait cannot be made for the time T3 and thefifth embodiment cannot be applied.

FIG. 12 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10; and

(2) after the move stops, irradiate the workpiece 10 with a laser beamat the position as long as the time T3 under the work stop conditions.

(Embodiment 6)

FIG. 13 is a process flowchart in a sixth embodiment of the invention.As an alternative method for handling an uncut portion in the bottomface of a workpiece, a backward move on the program path may be madefrom the work stop position for again working on the workpiece beforethe work stop position. However, if the work speed is fast, the actualwork path may deviate from a move command because of the servo followingability, etc. In this case, if a backward move on the program path ismade, it is not returned as the cut path before the work stop, and thebackward move position does not exist on the cut path. If the positionis irradiated with a laser beam, work failure occurs. The sixthembodiment is provided for taking countermeasures against it. When awork continuation command is given, a work condition command sectionselects work conditions for backward cutting at step S214 in response towork restart information from an interrupt/restart determination sectionand restores the functions required for work such as work gas sprayingand laser beam irradiation to the state before the temporary stop atstep S215. Next, a move command section makes a backward move on theprogram path by distance L2 at step S216. Therefore, even if thebackward path deviates from the cut path made before the work stop, abackward move is made while the workpiece is being cut at step S216.Next, the work condition command section restores the work conditions tothe original cut conditions at step S217 and the move command sectionstarts a move in the original direction again following the programpath, whereby the state becomes as if the work were continued nonstop,preventing work failure from occurring.

FIG. 14 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) irradiate the workpiece 10 with a laser beam under backward moveconditions for cutting the workpiece 10 by the distance L2 on thereverse program path; and

(3) cut the workpiece 10 following the program path under the originalwork conditions.

(Embodiment 7)

FIG. 15 is a process flowchart in a seventh embodiment of the invention.The first to sixth embodiments can provide countermeasures against anuncut portion in the bottom face of a workpiece. However, if a change ismade from the low-output work restart conditions or the laser beamirradiation stop state to the original cut conditions, it takes time instabilizing of laser oscillator output and the heat lens state of a lensin a work head and a mirror in the oscillator. Therefore, if cutting isstarted immediately after the conditions are changed, work failure mayoccur. The seventh embodiment is provided for taking countermeasuresagainst it. Steps S200 to S204 in FIG. 15 are the same as those in FIG.2. The laser beam irradiation time is measured with a timer 26 and atstep S218, a wait is made for move start at step S204 for predeterminedtime T4. Meanwhile, the laser oscillator output and heat lens state arestabilized.

FIG. 16 shows the working method in the embodiment.

(1) Interrupt the work at position A of workpiece 10 and then restartthe work;

(2) cut the workpiece 10 following the program path by distance L1 underwork restart conditions;

(3) irradiate the workpiece 10 with a laser beam under the original workconditions at and wait for the time T4; and

(4) cut the workpiece 10.

(Embodiment 8)

The optimum numeric values of the distances L1 and L2 and the times T1to T4 in the first to seventh embodiments vary depending on theworkpiece. Therefore, fixed values cannot cover different workpieces andit is inconvenient to set the values in parameters each time. To takecountermeasures against it, FIG. 17 shows an embodiment wherein theparameters such as L1 are added to the work condition data correspondingto workpieces. The work condition data as shown in FIG. 17 is registeredfor each workpiece. Which work restart type in the embodiments toexecute is set in data 28. If 0 is set, the process shown in theembodiments is not executed. Since workpieces like thin plates do notrequire any process shown in the embodiments, 0 is set. The distances L1and L2 and the times T1 to T4 are set in data 29 to 34. The sameworkpiece may or may not require the processes shown in the embodimentsdepending on the cutting speed. If the RAM capacity has a margin, thedata pieces 28 to 34 may be set in the conditions of the first conditiongroup and later.

According to the invention (aspects 1-4 and 8), to once stop the currentcutting being executed in automatic running and then restart the cuttingat the stop position, the workpiece can be worked on under optimumrestart work conditions, such as low speed and low output, at apredetermined distance after the restart or at the position withoutgiving a new restart work condition command, thereby removing the bottomface cut lag behind the top face of the workpiece, smoothing a flow ofmolten metal, and suppressing work failure at the restart work time.

According to the invention (aspects 5-7), to once stop the currentcutting being executed in automatic running and then restart the cuttingat the stop position, the cooling time and/or the laser beam stabilizingtime can be provided before the work is restarted under optimum restartwork conditions and a return is made to the work command operation basedon the work program command without giving a new restart work conditioncommand. Thus, the bottom face cut position lag behind the top face ofthe workpiece is lessened for smoothing a flow of molten metal, andoverheating prevention and/or laser beam stabilization are intended forsuppressing work failure at the restart work time.

According to the invention (aspect 9), to once interrupt the currentcutting being executed in automatic running, the workpiece is worked onunder optimum interrupt work conditions and the bottom face cut positionlag behind the top face of the workpiece is removed without giving a newinterrupt work condition command before the work is interrupted. Thus, aflow of molten metal is smoothed at the work restart time and workfailure at the restart work time is suppressed.

According to the invention (aspect 10), to once stop the current cuttingbeing executed in automatic running and then restart the cutting at thestop position, the workpiece is cut while a backward move on the movingpath by a predetermined distance under backward move work conditions,and then the cutting is continued again in the original work directionunder the original work conditions. Thus, the cut face at the workrestart time is prevented from becoming discontinuous and the quality ofthe workpiece is improved.

According to the invention (aspect 11), to change laser beam irradiationoutput from low to high output during cutting in automatic running,moving is stopped at the output change position and the workpiece isirradiated with a high-output laser beam for a predetermined time, thenthe move is restarted. Thus, the work can be restarted in the state inwhich the laser beam applied to the workpiece is stable, and the qualityof the workpiece is improved.

What is claimed is:
 1. A laser beam machining method for irradiating aworkpiece making a relative move in accordance with a work program witha laser beam for cutting the workpiece, to interrupt the cutting beingexecuted and restart the cutting at an interrupt position, said methodcomprising the steps of:(a) after restart of the cutting; working on amoving path specified in the work program under restart work conditions;(b) determining a total distance through which the workpiece moves underthe restart work conditions as a restart work distance, (c) comparingthe restart work distance with a predetermined distance L1; (d)continuing the working under restart conditions of step (a), thedetermining of total distance of step (b) and the comparing of step (c)until the restart work distance matches L1; (e) changing the restartwork conditions to original work conditions for continuing the cuttingwhen the restart work distance matches L1.
 2. The method of claim 1,wherein the restart work conditions comprise a lower irradiation outputthan the original work conditions and wherein said step (e) comprises asub-step of pausing the workpiece for a predetermined time to permitstabilizing of the lower irradiation output back to the original workconditions and then moving the workpiece to continue cutting after lapseof the predetermined time.
 3. A laser beam machining method forirradiating a workpiece making a relative move in accordance with a workprogram with a laser beam for cutting the workpiece, to interrupt thecutting being executed and restart the cutting at an interrupt position,said method comprising the steps of:cutting the workpiece while making abackward move of a moving path before an interrupt specified in the workprogram by a predetermined distance under backward move work conditions;and continuing cutting the workpiece again in an original cuttingdirection under original work conditions.
 4. A laser beam machiningmethod for irradiating a workpiece making a relative move in accordancewith a work program with a laser beam for cutting the workpiece, saidmethod comprising the steps of:stopping a work path move of theworkpiece for a predetermined time as a work condition is changed from alow-output laser beam to a high-output laser beam, wherein thepredetermined time corresponds to a stabilizing time for the high-outputlaser beam; and irradiating the workpiece with the high-output laserbeam.